This invention relates to additive compositions, in particular for fuels comprising at least one nitrogen-containing product incorporating two terminal imide rings and at least one polyglycol which is soluble in the said fuel, as well as preferably at least one detergent-dispersant. These compositions can be used as multipurpose additives for fuels and in particular for fuels used in spark ignition engines.
The use of conventional fuels very frequently leads to fouling of various parts of the engine as a result of incomplete vaporization and combustion of the fuel in the inlet system and in the combustion chambers.
In particular, in the case of spark ignition engines the formation and accumulation of deposits in the combustion chambers disturbs normal engine operating conditions.
These deposits significantly alter of heat transfer between the combustion chambers and the engine's cooling system by forming a layer of an insulating nature.
This results in an increase in the temperature within the chambers the feed gas mixture enters. Self-ignition of these gases is thus promoted, which gives rise to the appearance of the well-known phenomenon of engine knock.
In addition to this, the accumulation of these deposits in the combustion chambers may result in a reduction c,f the volume of the combustion zone, which is then reflected in an increase in the engine's compression ratio. This also promotes the occurrence of knock. In addition to this, the deposits which form in the various parts of the engine in contact with the fuel can partly absorb some of the fuel, thus contributing to a change in the fuel-oxidant mixture, with a stage of fuel impoverishment during absorption and a stage of fuel enrichment when the fuel is desorbed. Such a fluctuation in the richness of the fuel-air-mixture prevents the engine from operating under optimum conditions.
Whereas, periodic expensive cleaning of the affected parts of the engine, in particular the valves, may be carried out at intervals in order to deal with the fouling, the accumulation of deposits within engines and in particular on inlet valves may also be reduced by using fuels containing certain additives, for example additives of the detergent type which may for example be combined with corrosion prevention additives or additives preventing combustion chamber deposits.
The additives, which are well known in the trade, for example those of the polyisobutene-amine type, are normally associated with a mineral or synthetic oil and can cause increased fouling of combustion chambers and therefore an increase in the engine octane requirement, with a greater sensitivity to knock.
Of the many additives described in the prior art mention may be made of the condensation products of polyalkenylsuccinic anhydrides with polyamines, such as, for example, tetraethylenepentamine, which are in particular described in U.S. Pat. No. 3,172,892. These additives provide satisfactory results from the point of view of corrosion prevention properties, but are not effective as valve detergents.
Mention may also be made of the condensation products of polyalkenylsuccinic anhydrides with hydroxyimidazolines, in particular with 1-(2-hydroxyethyl)imidazolines substituted by an alkyl or alkenyl group in the 2 position, such as those described in patent application EP-A-74724. The products described in this application are satisfactory additives for engine fuels and have a significant corrosion preventing effect, but are not very effective from the point of view of carburetor detergency.
Combustion chamber fouling occurs progressively with the operation of an engine. An engine is characterised by its octane requirement, which corresponds to the minimum octane number of the fuel required by the engine in order to operate without knock. When the value of the engine's octane requirement exceeds the value of the octane number of the fuel used to operate the engine, in particular as the result of combustion chamber fouling, the phenomenon of knock is observed. The increase in the octane requirement of the engine is conventionally, for those skilled in the art, the phenomenon of ORI, named after the English abbreviation for "Octane Requirement Increase".
In order to restrict the occurrence of knock and its adverse consequences on an engine such as increased fatigue and wear on its vital parts, an excessively high engine octane requirement can be remedied by using a fuel which has a higher octane number than that previously used, subject to availability and a higher cost, The combustion chambers may also be cleaned out at intervals in order to remove the deposits formed and reduce the engine's octane requirement. This operation is however time-consuming and very costly.
Many patent documents describe additives which can be used in particular in engine fuels. Compositions such as those described for example in patent application EP-A-327097 have satisfactory anti-ORI properties, but relatively limited detergent properties. In addition, these compositions are not described as having good corrosion prevention properties.